The government is ready to support calls by the police for tougher anti-terror laws, including an extension of the 28-day limit for holding terrorist suspects without charge.

Gordon Brown yesterday threw his weight behind a call by the Metropolitan police commissioner, Sir Ian Blair, for sweeping changes, including new rules allowing suspects to be interviewed after charge and the use of security service phonetap evidence in court.

In a chilling account of the scale of the terrorist threat facing Europe, Sir Ian said "the sky is dark" and claimed the British criminal justice system was creaking under the impact of the terror trials.

He complained of the inflexibility of the system: "One major conspiracy will have taken two years and eight months to reach its court date, if it starts then: a current trial is likely to last over twelve months. The contrast with the speed with which the Netherlands dealt with the murderer of Theo van Gogh is striking."

Sir Ian argued the slowness with which trials were coming to court, and the restrictions on reporting, were contributing to the government's difficulties in convincing sceptical British muslims that a terrorist ideology had gripped many young British muslims.

Both Mr Brown and the deputy prime minister, John Prescott, backed Sir Ian's call for an extension of the 28-day limit, with the chancellor accusing the Tory leader, David Cameron, of simply not understanding the scale of the threat.

Mr Brown said the fight against terrorrism would be his number one priority if he became prime minister, adding he "completely agreed" with Sir Ian.

Senior government figures have returned to tough language on terrorism since the MI5 chief, Dame Eliza Manningham-Buller, issued a stark warning last week that her agents were tracking 30 serious plots to commit atrocities in the UK and abroad. The home secretary, John Reid, is reviewing Britain's anti-terror structure and the circumstances in which telephone tapping evidence compiled by the security services could be used in court. The conclusions are due this year.

Behind the scenes, ministers are anxious not to repeat the parliamentary debacle over the 28 days issue which inflicted a wounding Commons defeat on Mr Blair last year. After a long parliamentary battle, the government won the support of MPs for an extension from 14 to 28 days, but failed to win backing for 90 days.

Mr Reid is committed to introducing a new terror bill to consolidate the confusing patchwork of emergency counter-terror measures that have been enacted since 2000. Such a bill would be a major piece of legislation in itself, and ministers are undecided on accompanying measures - and whether they should be in a separate bill.

The home secretary believes it is up to the police to produce the evidence to persuade MPs that the 28 days should be extended.

With the Queen's Speech set to be dominated by security issues on Wednesday, the shadow frontbench refused to be thrown on the backfoot by the virulence of Sir Ian's call. The Conservatives would look again at the case for longer detention on the basis of evidence provided by the police, they said.

The shadow home secretary, David Davis, said the "arguments [in favour of a 90-day limit] I have seen so far both in public and in secret are worse than not great. They are dreadful."

The shadow attorney general, Dominic Grieve, said: "One of the difficulties we have is that we have a government that tells lies ... it is incredibly difficult to have a rational debate with them about what is needed."

Mr Cameron again proposed a minister solely responsible for terrorism as a full cabinet member alongside the home secretary.

The idea has been ruled out by Mr Brown, but he does favour the idea of a single budget for security, spanning the work of police and security services.

Sir Ian is clearly preparing to repeat his previous lobbying of parliament to demand the right to detain suspects for longer. He pointed out that the police had seized evidence apparently representing 100,000 different identities during arrests in the summer .

But as the parties traded rhetoric, a report published today warns that the government's counter-terrorism policy is being damaged by ministers' vote-seeking and party political interests.

The Joseph Rowntree Reform Trust study says sensible plans to combat terrorism are being "submerged" by the government's "electoral motives". It accuses Tony Blair and Mr Reid of playing to a tabloid agenda and "trying to win over the white working-class vote".